7circle wrote: I thought at first you where just adding the bits to a spare board as you only need one in the circuit.

But your Pin1 uTxm on IC1 has swapped with Byp on Pin6 and the designators are all different. (R8,9,10,11,15 .. and others)

Sorry. I should not have referred to that rev32 schematic. Too confusing. I only meant that the top section, which I omitted from the schematic posted today, was the same.

Looks like your putting the CellV straight in with out divider.
(Sorry I'm nosey)

Thanks for taking an interest. "Cell+" is the cell voltage. "CellV" is perhaps a poor choice of name for the divided voltage to be compared against the 1.5 V reference.

We need to use the 1.5 V reference because wqe want everything to work down to a cell voltage of 1.8 V. We should put "1.5 V" on the schematic.

I take it the JP11 is not connected for Current Sense.
It must be for Cell No 1.

Each ordinary BMU measures the voltage between its cell's negative terminal and the positive terminal of the preceding (more negative) cell. The first (most negative) cell has no preceding cell so there will be nothing connected to its link-in (LI) terminal (JP11) and so the associated analog input can be used for current measurement instead, via a shunt and the differential amplifier.

The current shunt must be connected to the negative terminal of the cell carrying the diff-amp board, by a short thick power cable, as the common mode range of the opamp only goes 300 mV below GND.

You may need slower filtering for your AD rate.
I thought very slow like 10 samples a second with filter would work.

-3dB frequency is 1/(2pi*RC)
= 10.6 Hz

What happens if their is 2000A in shunt or wild voltages?
The is it worth clamping Op- and Op+ with diodes.
Probably not worth it with 15k R21 and R22 and MCP6001 has +/-2mA on the pins and ESD ratings on all pins.

Agree not worth adding diodes as it can take +-30 V as it is. For an actual shunt current to produce that would require 120kA. But we must never disconnect the high current cable before disconnecting the sense wires.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Thanks 7circle, but you have two 150k resistors where there should be two 300k resistors and the shunt is 200A 50 mV so that's 250uR. I believe the circuit will operate up to 300A with up to 750uR between the shunt and GND since the MCP6001 input common mode range goes 300 mV outside the rails.

We intend to connect the + side of the opamp to the side of the shunt nearest GND since charge currents are generally much smaller than discharge currents.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Johny wrote: Lick, slurp, drool... Now if this one doesn't fit here is my postal address....

We'll send you the first one (Control Techniques SP5402) for $6k (less than half price). It'll take an 800 V battery where the Tritium will only take 450 V. Essentially the same peak power rating. Would suit a commercial vehicle AC conversion.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

7circle,
Re the FAN net, we deliberately sacrificed it to make the diff-amp mod work. The constraints of maintaining hazardous-voltage creepage distances and the ability to rotate the middle section of the board to make the two different isomers were too much to allow yet another signal to emerge from the middle section. But we can connect the fan up with a wire jumper if we need to.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Johny wrote: Lick, slurp, drool... Now if this one doesn't fit here is my postal address....

We'll send you the first one (Control Techniques SP5402) for $6k (less than half price). It'll take an 800 V battery where the Tritium will only take 450 V. Essentially the same peak power rating. Would suit a commercial vehicle AC conversion.

Um - thanks for the offer but I thought it was a bit big (physically) when you bought it. I suggest sticking it on eBay.

Johny wrote:Um - thanks for the offer but I thought it was a bit big (physically) when you bought it. I suggest sticking it on eBay.

Yes. I was joking, about sending it to you, but thought I'd take the opportunity to put the offer out there. It will overvoltage an induction motor more than the existing Tritium drive will, and will therefore get a higher power-to-weight ratio from the motor, and it would be fine in the back of a van. Comes with application processor module and software to allow programming a natural accellerator response. I'll probably put it up on eBay soon.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Thanks Mal, but we decided against Hall effect transducers due to their offset and drift.

7circle wrote:Also P2.6 is tied to oV. Why?
And Pd.2 is NC (... No Connect) it might be worth adding CAP & res foot prints if they are needed in the future.

Also JTAG pins are not used for anything else ... I'm sure I could think of something....

P2.6 was sacrified to get more thermal conductance between the cell terminal and the thermal pad on the micro, in the hope of getting more accurate cell temperature measurement from its internal tempoerature sensor.
P2.7 has now been reinstated as part of the "Fan" net. Thanks.
The JTAG pins don't have any other functions (except JD is also Reset).

Allowance for External Temp sensor could be a good wish too.
Even as a digital signal not analogue could be valuable.

Good idea, but no spare pins with analog input function (P2.6 and P2.7 no analog). I suppose we could swap the functions of P1.1 (Byp) and P2.7 (Fan) and then the fan line could be used as an input by omitting the Fan MOSFET and jumpering, but the changes to both hardware and software are too daunting at this stage.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

7circle wrote:Also P2.6 is tied to oV. Why?
And Pd.2 is NC (... No Connect) it might be worth adding CAP & res foot prints if they are needed in the future.

Also JTAG pins are not used for anything else ... I'm sure I could think of something....

P2.6 was sacrified to get more thermal conductance between the cell terminal and the thermal pad on the micro, in the hope of getting more accurate cell temperature measurement from its internal tempoerature sensor.

Wow, that's a big effort to get thermal coupling. [Edit: Thought thermal pad was for temperature monitoring of a single pin and pad was in the CHIP. But the thermal pad is under the CHIP and solders it to the PCB]

Interesting, where did you pick up that valuable info?

Will you use adhesive under the chip to hold it down before soldering?

Also the Shunt wiring could have holes for strain relief of twisted pair wires that are soldered to PCB.

Top work W&C your in a field of your own. With lots of green grass.

7¢

[Edit - Comment on thermal pad]

Last edited by 7circle on Sat, 27 Nov 2010, 07:31, edited 1 time in total.

Don't mean to be pedantic, {edit : I just noticed the arrows on the BMU's}

The Labeling of the PCBs as
BMU Ver 44
BMU Ver 45
[Edit: ... makes it look like the same PCB type but different versions.
It would be obvious when still linked as strip of BMU PCB's but when separated it would look like newer versions.]

If others where to use it [Edit: even your scrap through outs, that some of us can't help but hoard] would it be worth using extra detail, some thing like
BMU +<>- SHUNT Ver 45
BMU -<>+ TXOPTO Ver 44
[Edit ... and better apply the same version Number]

Will you have BMU pcbs in the panel that are say [Edit: for opposite direction]
BMU +<>- TXOPTO
BMU -<>+ SHUNT

Four different PCB's is stretching your patience.

And Nightmare to build. But if you need the variety to build odd battery groups.

As its unlike ly to have only two Batteries in a group if the two end ones in your strips of 8 or 9 squiggle linked PCB's is has the same option it gives you the option to cut off the one you don't need and still have the next BMU with the TXOPTO or the SHUNT where you need it without having to fit wires between the PCBs on the ends.

Don't mean to be pedantic, {edit : I just noticed the arrows on the BMU's}

The Labeling of the PCBs as
BMU Ver 44
BMU Ver 45
[Edit: ... makes it look like the same PCB type but different versions.
It would be obvious when still linked as strip of BMU PCB's but when separated it would look like newer versions.]

Fixed. Thanks. Will use same version number on all flavours and isomers from now on.

If others where to use it [Edit: even your scrap through outs, that some of us can't help but hoard] would it be worth using extra detail, some thing like
BMU +<>- SHUNT Ver 45
BMU -<>+ TXOPTO Ver 44
[Edit ... and better apply the same version Number]

Are you suggesting we add the text "+<>- SHUNT" preceding the version number? If so, it seems unnecessary since one flavour will have the text "shunt" and the other "iTX" near their respective i/o pads, and there are already big + and - near the cell terminals.

Will you have BMU pcbs in the panel that are say [Edit: for opposite direction]
BMU +<>- TXOPTO
BMU -<>+ SHUNT

Four different PCB's is stretching your patience.

And Nightmare to build. But if you need the variety to build odd battery groups.

As its unlikely to have only two Batteries in a group if the two end ones in your strips of 8 or 9 squiggle linked PCB's is has the same option it gives you the option to cut off the one you don't need and still have the next BMU with the TXOPTO or the SHUNT where you need it without having to fit wires between the PCBs on the ends.

And another string on the panel would start with the other isomer of the diff-amp board:
BMU -<>+ SHUNT (1)

But we're looking into getting someone to assemble the boards for us using a pick & place machine and so this may change depending what they tell us to do to make it cheaper. May only have strings of 4 or something. May have plain vanilla flavoured boards in the middle (neither iTX or shunt layout). [Edit: May have P&P do them all as plain vanilla and we add the special flavours to a few of them later.]

Also looking at redoing the artwork in Cadsoft EAGLE instead of Protel 99SE.

Last edited by weber on Thu, 25 Nov 2010, 07:53, edited 1 time in total.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

Motor mounting bracket
Last EV day we worked on the bracket to adapt the induction motor feet to the original ICE rubber engine mounts. Before sending the motor off for machining of the shafts at Ultramotive and testing at Tritium, we had made a prototype bracket out of 50x50x5 mm steel angle. Cut, scored and bent to the correct angles and tack-welded. It was time to see how it fitted. That's 95 kg of motor and 35 kg of gearbox.

In the first photo below, you can see a thin power-steering hydraulic-pipe that the motor foot is touching. So we lifted the motor enough to use a sabre-saw and file to cut away part of the motor foot to give the pipe some clearance.

The blue electrical tape is to hold in place a black rectangular steel "cup" that surrounds the rubber mount, presumably to ensure the motor remains in place even if the rubber tears, or perhaps to limit the travel so the rubber doesn't tear.

When we tried to install the PPF ("Power Plant Frame" -- the aluminium beam that connects the diff to the gearbox and is the gearbox's only support) we found it was 12 mm too short. In other words we needed to adjust our bracket to move the motor and gearbox 12 mm toward the rear of the car. So out it came and some "ears" were welded on and new 12 mm holes drilled, 12 mm from the old ones. Also the bends were fully welded since the angles were clearly correct, and the excess length was removed from the bent-up ends.

Here is the bracket with ears, and with the rubber mounts bolted on, but without the cups. The cups had to be partly cut away at the rear to provide clearance for the bracket which now overhangs them.

A second fitting allowed us to bolt in the PPF and prove that we had it correct in the front-rear direction.

Next I tried placing a mock-up of the battery box on top of the motor (partly made and held together with clamps). I carefully closed the bonnet and got underneath with a light, to reach up and check bonnet clearance. There was enough bonnet clearance at the back corners (near the firewall), but there was essentially zero at the front corners.

Then I noticed that the engine mounting bolt, to the chassis, on the drivers side, was not sitting all the way down in its slot. It was about 10 mm high. I realised that the only way to allow it to sit all the way down was to shorten our mounting bracket side-to-side.

So off came the PPF again and out came the motor and gearbox -- all the way out and onto the concrete and rolled upside down.

A bit of trigonometry told me that I had to shorten the bracket by 5 mm. So I cut 5 mm out of the middle and then welded it back together. After grinding back with a flap-disk, you would never know it had been cut.

So the chamfer on the back feet will have to be a lot bigger now. I have marked them but not cut them. I thought I'd better give the neighbours a rest from the noise, it being 8 pm and all.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

The next stage in making the motor mounting bracket was to effectively turn it into a gearbox mounting bracket. This is so that in low gears the multiplied torque reaction from the gearbox goes directly to the chassis (via the rubber mounts) and does not have to pass through the motor flange. The aluminium motor flange and the four M8 bolts holding it to the body of the motor look like they are engineered to within a millimetre of their life, to barely take the motor torque (350 Nm).

So we welded a sort of "box" made out of pieces of 5 mm thick angle onto the bracket. This is then bolted to the gearbox adapter plate. It then becomes almost incidental that the motor feet also happen to sit on the bracket. The last photo shows the motor and gearbox upside-down, with the bracket bolted in place.

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

The flywheel was delayed because, as first delivered, the outer ring where the pressure-plate is mounted was 10 mm thick while the inner area where the clutch plate is gripped was 9.5 mm thick. It was supposed to be the other way 'round. This was rather surprising since we supplied not only a proper workshop drawing, but also the original flywheel which should have made the direction of the 0.5 mm step obvious. Also the pressure-plate bolt holes in the flywheel were tapped to an ordinary M8 thread instead of the M8 fine thread that the drawing (and the supplied bolts) called for.

So some ordinary M8 bolts were supplied and it went back into the lathe to put the step the right way 'round, by taking a whole millimetre off the outer ring. So the flywheel is now 0.5 mm thinner than it should have been, which is unlikely to be a problem.

The first photo shows the original clutch plate and pressure plate, which will be reused, the standard 2517 Taper Lock bush with 38 mm bore and keyway, and the new flywheel.

Below you can see Coulomb measuring the "critical dimension" which was measured off the original ICE long ago -- the distance from the flywheel face to the engine face that mated with the gearbox bellhousing. So we need to reproduce that from flywheel face to adapter-plate face. This needs to be 38 mm for the MX-5. There is a certain amount of trial and error in achieving this with a Taper Lock fitting and we settled for 37.5 mm.

Next you can see Coulomb tightening the grub screws in the Taper Lock bush to the correct torque with a 100 mm long Allen key, by attempting to lift himself off the ground. (It required twice the maximum torque setting of our 1/4" drive torque-wrench and we didn't have the right adapters to adapt an Allen key bit to our 1/2" drive torque-wrench.

Here's a closeup of the Taper Lock bush. You can see we're part way through drifting a teflon-and-tin plain-bearing into the hole we had bored in the end of the motor shaft. This bearing will support the end of the gearbox input shaft. It replaces a ball bearing that was set into the original flywheel and is only slightly smaller in diameter than the electric motor shaft.

Now the bearing is all the way in. We used wood between the bearing and the hammer for most of the drift and then finally some aluminium.

You can also see the pressure-plate with the black plastic clutch-plate-alignment-tool sticking out of it. This holds the clutch plate centred on the pressure plate while they are bolted to the flywheel.

Next we have the pressure plate bolted to the flywheel and torqued up, with the clutch plate sandwiched in between. And we move the gearbox into position.

The questions now are, have we got the clutch plate centered properly and have we designed the adapter plate correctly, and have we cut the motor shaft to the right length so that the gearbox input shaft will slide far enough into the teflon-and-tin plain bearing, but not too far, and in proper alignment?

The answers are yes, yes and yes! It went together absolutely smoothly. You wouldn't have even known there was anything that had to align inside. The bell-housing just slid onto the adapter-plate dowels the same as it has every other time we've put it together, when there was no motor shaft or clutch in place.

What a joy it was to put it in fourth gear and turn the pulley on the non-drive end of the motor and feel the gearbox output shaft following it, with no noticeable noise or friction.

Coulomb commented that it is starting to seem more like a car instead of a science project. Woohoo!

One of the fathers of MeXy the electric MX-5, along with Coulomb and Newton (Jeff Owen).

EV2Go wrote: Ahh ok well that should be hard enough to resist wear. Any reason you didn't use something like 6061 Alloy to reduce weight, since EV don't require reciprical mass?

Sorry. I didn't realise you meant Aluminium alloy. The main reason is the Taper Lock shaft fixing. I assumed that an off-the-shelf Taper Lock bush, which is steel, had to be used with a steel hub, based on this engineering document.

Now that I google "Aluminium taper lock" I find a few mentions of aluminium hubs, but these mostly seem to be for fans or pulleys driving fans which aren't exactly high-torque applications.